Thermoplastic resinous material has been melted and applied as a thin layer to sheet material such as shoe parts and cooled to provide a resilient stiff layer. This procedure is shown for use in stiffening the toe and counter portions of a shoe upper in the U.S. Patent to Chaplick et al. U.S. Pat. No. 3,316,573 issued May 2, 1967. The stiffening has been found effective to insure shape retention of the sheet material such as shoe parts with which the resinous material is associated. However, particularly with heavier shoes or boots, greater strength and stiffness has been desired.